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The objectives of this study were to use the in vitro gas production (IVGP) technique to evaluate the pattern and parameters of anaerobic fermentation of forages from south Texas pastures throughout the year to (i) obtain empirical relationships between the IVGP technique fermentation parameters and chemical composition of the forages and (ii) develop equations to compute total digestible nutrients (TDN). During four consecutive years (2006-2009), forage samples were collected monthly ( n = 39) at the King Ranch, TX, and chemical analyses and IVGP were obtained. For 2006, 2007, 2008 and 2009, the average lag times, h, were 6·47 ± 0·54, 7·75 ± 0·65, 7·49 ± 2·01 and 5·44 ± 1·46, and the average ratio of millilitre of gas per milligram of dry matter was 0·41 ± 0·11, 0·34 ± 0·09, 0·34 ± 0·07 and 0·26 ± 0·10 respectively. There was a moderate negative correlation ( r = −0·53) between lignin and neutral detergent fibre (NDF) and a moderate positive correlation ( r = 0·58) between crude protein and NDF digestibility. The predicted fractional passage rate (kp) by the large ruminant nutrition system model using the level 2 solution was on average 0·0366 h−1. The average computed TDN assuming a kp of 0·04 h−1 was 55·9%. We concluded the IVGP technique may be used to predict TDN values of warm-season forages. [ABSTRACT FROM AUTHOR]

Cool-season annuals may fill gaps in seasonal forage availability and reduce stored feed needs for beef cattle producers in the Southeast. These forages can be established during the autumn via sod-seeding or broadcasting on warm-season perennial grass pastures such as bermudagrass and bahiagrass or planted into a prepared seedbed. Opportunity exists to use small grains that vary in their individual growth distribution to extend the grazing season. Small grains adapted to the region include cereal rye (Secale cereale), wheat (Triticum aestivum), oats (Avena sativa), and triticale (×Triticosecale). These species provide bimodal forage dry matter (DM) production during the autumn and early winter months, and can be grown in monocultures or mixtures. Cereal rye generally provides forage DM earliest in the season, followed by triticale, wheat, and oats. Fall production potential of these species is primarily dependent on planting method, seeding date, fertility, and variety selection. These species provide high quality forage DM that may support animal performance in stocker and cow-calf operations with minimal supplementation, and can be grown in combination with annual ryegrass and/or legumes to further lengthen the window of grazing. Annual ryegrass and legumes in the Southeast includes coldtolerant and rust-resistant diploid and tetraploid varieties of ryegrass, and adapted true clover (Trifolium sp.) varieties. Autumn-planted ryegrass and/or clovers including primarily crimson, arrowleaf, ball, and white clover, provide minimum to nonexistent forage mass for grazing during the fall. Naturally reseeding ryegrass or clovers will often provide earlier forage mass; however, DM is usually not adequate for stocking until late-January through May. With appropriate levels of N fertilization, ryegrass produces more forage DM, and thus allows for earlier stocking and greater stocking rates compared to clovers. Tetraploid varieties of ryegrass, when seeded into prepared seedbed, can provide adequate forage mass for fall grazing. Earliness of forage mass for stocking of clover ranges from crimson (earliest), to arrowleaf and ball (mid), to white clover (latest). White clover, however, in adapted soils and with adequate spring-summer rainfall and proper stocking rate, can provide grazing during early to mid-summer months. From the first frost event in late fall through the early spring months, cool-season annual forages provide actively growing forage to extend fall and spring grazing for cow-calf and/or stockers during winter dormancy of perennial grass pastures. [ABSTRACT FROM AUTHOR]

The forage-animal interface is a vital component of agricultural systems that is often overlooked by both agronomy and animal science programs. As such, current grazing models do not always provide a satisfactory understanding of how forage species and/or cultivars respond to livestock interaction in both production and physiology, how forage can influence the animal, and how the nexus of these two entities may affect the environment. The objective of this effort was to develop a conceptual framework of a dynamic model that combined the forage and ruminant livestock interactions, and to provide the initial parameterization of a model for bermudagrass pastures. The systems dynamic methodology was used. The causal loop diagram (CLD) was first envisioned based on the hypothesis that not only can forage factors affect performance and behavior of the grazing animal, but the grazing animal, through its herbivorous behavior and selective intake, can affect and alter the physiology, growth, and performance of the forage and the pasture. Generation of a preliminary stock-and-flow diagram (SFD) with variable flight simulators was also performed. The main CLD was a composite of four sub-models that represented the agronomic, animal, atmospheric, and soil subsystems. The limitations of this model existed in the lack of meta-analytical publications in which necessary equations have been summarized that could be used in model programming. The parameterization of the model suggested that forage allowance was the driving factor in animal ADG, and forage growth rate was governed by a combination of evapotranspiration, defoliation, soil N, and precipitation. Our simulation of the bermudagrass scenario suggested that under these production conditions, most portions of the model operated in a traditional goal-seeking fashion. The initial results provided the documentation of the interface concept for the benefit of forage agronomy and animal nutrition programs as well as the foundation for advancements of the model to eventually serve as potential decision aid in production-economic strategies. [ABSTRACT FROM AUTHOR]